The requisite properties for the material of a fuel injector component such as a nozzle needle and a nozzle body defining a valve seat for the nozzle needle of a fuel injector for a gasoline engine include the wear resistance of the sliding parts, and the resistance against the corrosion due to the moisture contained in the fuel. Because the mass produced fuel injectors for gasoline engines are normally used for injecting fuel into an intake manifold of the engine where the prevailing temperature is no more than 150.degree. C., the nozzle needles and the valve seats of these fuel injectors are made of JIS (Japanese Industrial Standards) -SUS440C stainless steel which is hardened and tempered at a temperature lower than 200.degree. C.
As a part of the efforts to reduce the emission from engines, extensive research efforts have been directed to the development of lean burn engines. Some of the lean burn engines use fuel injectors which inject fuel directly into the cylinders or the combustion chambers of the engine. In such engines, part of each fuel injector is inevitably exposed to a combustion gas of high temperature, and the capability of the fuel injector to withstand heat is a major problem. More specifically, when fuel is directly injected into the combustion chamber of an engine, if the material for the fuel injector consists of the stainless steel tempered at low temperature, it will be further tempered during use. Therefore, for the material to retain its hardness and dimensional stability, it must be tempered at a temperature higher than 400.degree. C.
However, if the JIS-SUS440C is tempered at such a high temperature, the following problems will arise:
(1) Reduction in corrosion-resistance due to the precipitation of secondary Cr--Fe double carbides; and PA1 (2) Reduction in hardness and wear-resistance due to the softening resulting from tempering and the subsequent exposure to a high temperature during use.